The present invention relates generally to medical devices. More specifically, it relates to a mechanical imaging system and process for examining, mapping, and diagnosing diseases of a palpable organ such as a prostate gland in a male patient, especially the prostate cancer. It is also applicable more generally to mechanical imaging of palpable tissues, including but not limited to, through natural body openings in a human being, i.e. mouth, ear(s), rectum, and other body cavities. It is also applicable to determination of a relative stiffness or elasticity of tissues. The term “patient” includes humans and animals, both alive and dead that can be subject for mechanical imaging.
The high incidence of prostate cancer, as well as benign prostatic hyperplasia (BPH), especially among the older male population, dictates the need for effective means of early detection. Prostate cancer is the cause of death in about 30,000 men each year, making it the number two cancer killer of men in the United States, second only to lung cancer. However, if prostate cancer is detected early and treated effectively, the chance of survival of one afflicted with this disease improves significantly. Current methods of early diagnosis of prostate cancer include digital rectal examination (DRE), measurement of serum levels of prostate specific antigen (PSA), and transrectal ultrasound (TRUS) examination.
The following discussion provides useful overview of various methods described in the prior art and applicable to prostate examination and imaging.
Substantial prior art is accumulated describing various devices and techniques using ultrasound for the imaging of the prostate. U.S. Pat. No. 6,561,980 by Gheng describes the methods of processing ultrasound images to cause automatic segmentation of prostate, rectum, and urethra once the transverse cross-sectional image of prostate is acquired by ultrasound means. U.S. Pat. No. 6,824,516 by Batten describes a sophisticated system for examining, mapping, diagnosing, and treating prostate diseases based on ultrasonic imaging, this patent is incorporated herein in its entirety by reference. U.S. Pat. No. 6,778,690 by Ladak describes a method of processing 2D and 3D ultrasound images to determine the prostate boundaries and is also incorporated herein by reference in its entirety as it provides useful image processing methodology.
Unfortunately, to date the experience with TRUS as a means of prostate cancer screening and staging has been disappointing. It adds little to screening by DRE and PSA, and the small improvement in prostate cancer detection does not justify its cost. As a screening test, TRUS has a low specificity and a high false positive rate. Evaluation of pathologic specimens shows that a significant fraction of tumors are isoechoic and thus indistinguishable from surrounding tissue, while many palpable tumors could not be visualized by TRUS.
The most sensitive single test for prostate cancer is measurement of serum PSA levels. However, its positive predictive value is limited. The DRE alone is even less useful. However, combining the two modalities nearly doubles the cancer detection rate. Large-scale studies of systematic screening for prostate cancer using PSA, DRE and TRUS concluded that combining PSA and DRE provided the highest sensitivity and specificity for prostate cancer diagnosis. Therefore, the combination of the two methods for prostate cancer screening is currently recommended by the AUA and American Cancer Society, and has been approved by FDA for patients between the ages of 50 and 75 years.
At the present time, digital rectal examination is the most widely used method of prostate cancer screening. Approximately 30-50% of palpable prostate nodules prove to be malignant upon pathologic evaluation. Screening trials have demonstrated that 70% of men with abnormal DRE undergoing radical prostatectomy have organ-confined cancer. A strong association between abnormal DRE and prostate cancer mortality has been demonstrated and it was suggested that screening DRE could prevent as many as 50-70% of deaths due to prostate cancer. DRE also has been shown to be the most cost efficient prostate screening method, especially when combined with PSA.
The main disadvantage of DRE is its high degree of subjectivity. The user has to instinctively relate what he or she senses by the finger to previous DRE experience. There may not be a sufficient number of skilled users available for large-scale mass prostate screenings. Another limitation of DRE is that a physician performing the examination cannot objectively record the state of the examined prostate. Therefore, it is difficult to objectively compare the results of consecutive examinations of the same prostate.
A new method of prostate imaging based on principles similar to those of manual palpation has been developed by Sarvazyan et al. and described in the U.S. Pat. Nos. 6,569,108; 6,142,959; 5,922,018; 5,836,894; 5,785,663; and 5,524,636, all incorporated herein in their entirety by reference. This method, termed Mechanical Imaging, provides the ability to “capture the sense of touch” and store it permanently for later temporal correlation and trending. The essence of mechanical imaging is measurement of the stress pattern on the surface of the compressed tissue and analyzing the changes of that pattern while moving the sensor array over the examined tissue. Temporal and spatial changes in the stress pattern provide information on the mechanical structure of the examined tissue and enable 3D reconstruction of internal structures and mechanical heterogeneities in the tissue. Mechanical imaging is free of many of the disadvantages of DRE. Mechanical imaging has been shown to exceed substantially the limits of lesion size and depth detectable by conventional manual palpation techniques [Weiss R., Hartanto V, Perrotti M, Cummings K, Bykanov A, Egorov V, Sobolevsky S. “In vitro trial of the pilot prototype of the prostate mechanical imaging system”, Urology, V.58, No. 6, 2001, p. 1059-1063].
Recently, the American Urological Association issued recommendations to help physicians confirm the diagnosis of prostate cancer. According to these recommendations, a biopsy should be considered for any patient with an abnormal DRE and elevated PSA. The effectiveness and reliability of DRE are highly dependent on the skill of the user, since the finger does not provide a quantitative or objectively verifiable assessment. Thus, there is a great need for a new technology and a device to enable general practitioners and urologists alike to perform a reliable, accurate, sensitive, and quantitative assessment of the prostate using a computerized palpation-imaging device. Moreover, such accurate assessment of prostate size, shape, and elasticity is also important for diagnosing and monitoring of prostate cancer and BPH. Mechanical imaging technology and the low cost, prostate imaging device should improve significantly the ability of minimally trained individuals in primary care settings to assess, screen, and monitor prostate pathology in a reliable and valid manner in a male human, with a minimum of physical and mental discomfort.
While prior art mechanical imaging devices provided for data collection, the ability to recreate the 2D and 3D images of the prostate were limited by the insufficiently accurate information about the position of transrectal probe with regard to the examined prostate in the course of examination. One reason for this is because the prostate can shift from its original place during the procedure. Therefore, the prior art methods have a fundamental disadvantage in that as the examination progresses, no means are available to properly compensate for the probe position and orientation relative to the moving prostate. Inaccuracies in the evaluation of the location of the prostate with respect to the probe head during the course of examination may result in low quality of obtained images and introduce various artifacts.
The need exists therefore for a prostate examination means and methods of use designed to eliminate the distortion in the position data of the prostate probe and make it independent of the internal movements of the prostate organ.